Wireless networks, such as wireless local area networks (WLANs) based on the IEEE 802.11 standard, have been widely deployed in many enterprises, primary to provide wireless data access from portable devices, such as laptop computers and personal digital assistants (PDAs), to the wired infrastructure of the enterprise. If an infrastructure-mode wireless LAN is to be deployed in a specific area, e.g., an enterprise facility, it is necessary to appropriately place wireless access points to which terminals associate. Since the coverage range of a single access point is limited, typical installations in enterprises consist of multiple access points. Since bad signal reception leads to unacceptable network behavior, such as insufficient overall throughput, adequate signal coverage throughout the area must be ensured.
A number of techniques have been proposed or suggested for determining the placement of access points for a wireless network. An important aspect of such techniques is determining the expected signal strength coverage of an access point if it were to be placed at a specified location at the site. Typically, such tools estimate signal strength coverage given an expected location for an access point based on an analytical radio propagation model. The model takes into account radio signal propagation, augmented with information about the number of walls and other obstructions in the signal path, as well as the material and other characteristics of the obstructions. This typically requires a detailed floor plan of the building with information about signal reflectors and obstructors in the floor plan.
U.S. patent application Ser. No. 10/776,058, filed Feb. 11, 2004, entitled “Estimating the Location of Inexpensive Wireless Terminals by Using Signal Strength Measurements,” assigned to the assignee of the present invention, and incorporated by reference herein, discloses a technique for determining the placement of wireless access points that (i) uses actual signal measurements, and (ii) requires no explicit knowledge of signal reflectors and obstructors. See also, P. Krishnan et al., “A System for LEASE: System for Location Estimation Assisted by Stationary Emitters for Indoor RF Wireless Networks,” Proc. of IEEE Infocom 2004 (March, 2004), incorporated by reference herein. In particular, a technique is disclosed for constructing a signal strength model for an existing access point, based on actual signal strength measurements of this access point at several sampling points. The signal strength model can then be used to predict the estimated signal strength from the access point at any point of the site.
A need exists for methods and apparatus for predicting the signal strength coverage of a wireless access point, given its desired location at a site. A further need exists for methods and apparatus for constructing a signal strength model without having actual measurements for the access point. In other words, a need exists for methods and apparatus for constructing a signal strength model for an access point at a random location within a site, without placing a real access point at the desired location and obtaining measurements.